1. Field of Invention
The present invention relates to an apparatus and a method for controlling a reaction which occurs in a reformer for reforming hydrocarbon and reformate fuel into a desired type of fuel with a high concentration of hydrogen.
2. Description of Related Art
A reformer designed to reform a vapor mixture of methanol and water into reformate gas mainly composed of hydrogen is known. In principle, according to a reforming reaction occurring in the reformer, methanol reacts with water vapor so as to produce hydrogen gas. In other words, a water vapor reforming reaction occurs in the reformer. This is an endothermic reaction, as can be understood from equation (1) shown below. EQU CH.sub.3 OH+H.sub.2 O.fwdarw.3H.sub.2 +CO.sub.2 -49.5 kJ/mol (1)
Further, the activation temperature of a reforming catalyst is relatively high (about 300.degree. C.). Therefore, in order to continue the above-mentioned reforming reaction, it is necessary to supply a corresponding amount of reaction heat.
On the other hand, as an example of a reforming reaction of methanol, there is a partial oxidation reforming reaction wherein hydrogen is produced through an oxidation reaction. This is an exothermic reaction, as can be understood from the equation (2) shown below. EQU CH.sub.3 OH+1/2O.sub.2.fwdarw.2H.sub.2 +CO.sub.2 +189.6 kJ/mol (2)
The reactions represented by the aforementioned formulas (1) and (2) can be caused to proceed simultaneously. For example, there is known a fuel cell system of a type compatible with partial oxidation, wherein the heat generated in the partial oxidation reaction compensates for the heat absorbed in the water vapor reforming reaction (Japanese Patent Publication No. HEI 7-57756).
As is apparent from the equations (1) and (2), the amount of heat absorbed in the water vapor reforming reaction is greatly different from the amount of heat generated in the partial oxidation reaction. Thus, provided that these reactions occur simultaneously for methanol of 1 mol, a large amount of heat is generated and the catalyst reaches an excessively high temperature, so that the catalyst may deteriorate in activity or durability. Conversely, if the partial oxidation reforming reaction (equation (2)) is at a low ebb, the reforming catalyst falls in temperature, so that an undesirably large amount of methanol remains and an undesirably large amount of carbon monoxide gas is produced.
That is, even in the case where the water vapor reforming reaction is caused to proceed simultaneously with the partial oxidation reforming reaction, the proceeding of the water vapor reforming reaction may be adversely affected depending on a degree of the proceeding of the partial oxidation reforming reaction. For this reason, the reformer of a type compatible with partial oxidation needs to suitably control the partial oxidation reaction. However, the above-described known apparatus do not control the partial oxidation reaction. Therefore, the known apparatus have trouble in constantly maintaining the reforming portion at a temperature required for the reforming reaction. In particular, in the case where the amount of reformate fuel fluctuates in response to load fluctuations in an energy converter such as a fuel cell which consumes reformate fuel, the temperature of the reforming portion such as the reforming catalyst may become unstable. As a result, the reformate gas may deteriorate in quality.